THE INFLUENCE OF ALLOYING ELEMENTS ON IMPURITY INDUCED GRAIN-BOUNDARY EMBRITTLEMENT

A nonequilibrium thermodynamic model which describes the effect of solute grain boundary segregation on grain boundary cohesion was extended to Fe ternary systems. According to the model, Mo, W, and Zr strongly reduce, Ni, Ti, and V slightly reduce, and Cr and Mn enhance impurity-induced grain boundary embrittlement in an Fe ternary system. Fe-P, Fe-P-Mn, Fe-P-Mo, and Fe-P-W alloys were studied by Auger electron spectroscopy, scanning electron microscopy, 4-point slow bend tests, and tension tests. The results show that for a given amount of P grain boundary segregation the grain boundary strength increases with increasing Mo or W grain boundary segregation and decreases with increasing Mn grain boundary segregation. These results showing the remedial effect of Mo or W, and the embrittling effect of Mn on P-induced grain boundary embrittlement are consistent with predicted results. The nonequilibrium model was also used to evaluate impurity-induced interfacial embrittlement in continuous fiber metal matrix composite materials.